Endogenous and exogenous endocrine factors

Abstract

The relationship between breast cancer risk and age at menarche, age at first pregnancy, use of birth control pills, and use of postmenopausal replacement estrogens is reviewed.

PIP: Breast cancer is the most common cancer in the United States comprising 30% of all cancers. There is strong evidence indicating that cumulative estrogen, and possibly progesterone, exposure of breast epithelial cells causes this cancer. After age 40 the sharp increase of cancer rate slows considerably. In industrialized countries the rate is 6 times higher than in Asia or Africa, however, ethnicity does not seem to be a major factor, as shown by studies on Japanese migrants to the U.S. Early menarche, before age 12, increases the risk fourfold, and higher levels of estrogen and progesterone found in daughters of breast cancer victims. Strenuous physical activity could delay menarche to 15.4 years of age, thus lowering the risk. Menopause lowers the risk, too, as does a shorter active menstruation history. Increased parity also decreases the risk, late first full-term pregnancy does the opposite. In parous women prolactin levels are lower, and sex hormone-binding globulin (SHBG) levels are higher. In older age weight gain also becomes a contributory factor. Estrogen plays a strong role in the genesis of breast cancer, and estradiol levels were 30% higher in cancer patients. Urinary estrogen levels were 36% higher in North American teenagers than in Asians. Fat intake and reserpine use can increase prolactin levels, however, its role is only putative, as is the role of progesterone. Increasing duration of use of oral contraceptives also raises the risk depending on age at first use and duration. Estrogen replacement therapy is similarly implicated, although a combination estrogen- progesterone therapy was beneficial. Furthermore, the benefits of estrogen to prevent osteoporosis and heart disease also have to be balanced against its carcinogenic potential.